1. Field of the Invention
The present invention relates to an image projection apparatus and a method of controlling the same.
2. Description of the Related Art
Recently, liquid crystal projectors that can simply and easily display a large screen by projection have come to be used widely in making presentations in meetings or displaying movie content at home. The liquid crystal projectors are used in various lighting environments, and it is desirable to carry out color reproduction according to actual lighting in projection environments. On the other hand, CIECAM02 (CAM: Color Appearance Model), which is a chromatic adaptation model, published by CIE and other models have been developed for color matching technology. Using these techniques and taking into consideration the lighting environments and the like of liquid crystal projectors, color reproduction is becoming a possibility.
To apply color reproduction to a liquid crystal projector by taking such visual adaptation into consideration, it is necessary to acquire information about illuminating light (ambient light) as viewing environment information. Existing techniques for measuring such illuminating light includes, for example, spectroscopic instruments that use diffracting gratings and color sensors which use color filters or the like. Furthermore, it is necessary to install an integrating sphere or diffuser on the front of the sensors in order to sense the illuminating light properly.
Such equipment, if used, will allow the illuminating light to be measured accurately, but is not desirable from the viewpoint of product costs. If the liquid crystal projector is equipped with a screen color measurement sensor (color sensor) for automatic screen color correction, desirably the illuminating light is sensed using the color sensor. Examples of measuring illuminating light using a color sensor includes a technique, described in U.S. Pat. No. 7,314,283, for projecting one or more calibration images and acquiring color information about the one or more calibration images using the color sensor. The technique performs color conversion in such a way as to match appearances of colors based on color information about an input image and color information about the projected image on a projection plane, thereby changes colors of the input image, and consequently obtains colors for use to output to the projector.
The method described in U.S. Pat. No. 7,314,283 measures the calibration image in advance and thereby obtains color conversion characteristics which realize both color correction on the projection plane and correction for the influence of ambient environment light. However, complicated computations are required in order to generate a 3D-LUT which realizes both color correction on the projection plane and correction for the influence of ambient environment light at the same time. Furthermore, if ambient illuminating light (ambient light) changes during projection, it becomes necessary to regenerate the 3D-LUT which realizes both color correction on the projection plane and correction for the influence of ambient environment light at the same time. This makes it necessary to carry out complicated computations again.